Technical Summary of Lunar Impacts of 1999 November 18
A summary of the seven confirmed lunar impacts is given in the table below. This is an ASCII plain text table that must be viewed with a fixed-space font such as Courier for the columns to line up properly. We are naming these with letters in the order of discovery. The UT date is 1999 November 18. In each case, the events were confirmed on my videotapes made at George Varros' backyard in Mount Airy, Maryland, and the timings are from my tapes. The early-reported estimates of the locations of D and E were rather far off in longitude, according to measurements of the video images made by Ben Wun and me on December 8.
Accuracy, Approx. Discovered Selenographic Name UTC sec. Mag1 Mag2 by Long. Lat. Description h m s F 3:05:44.89 0.02 6.2 9? David Palmer 65W 40N 180km se of Harding D 3:49:40.40 0.02 4.9 7 David Palmer 68W 3N w. wall of Hevelius E 4:08:04.10 0.03 5.8 8 David Palmer 78W 15S 140km SW of Rocca G 4:12:27.83 0.05 5.5 Gural/Dunham 90W 40S A 4:46:15.52 0.05 5.1 8 Brian Cudnik 71W 14N 30km NE of Cardanus B 5:14:12.92 0.02 6.2 8 Pedro Sada 58W 12N 150km E of Galilaei C 5:15:20.22 0.02 5.3 7 Pedro Sada 58W 20N 100km S SchiaparelliMag1 is the magnitude of the flash measured from my tape (relative to 4th and 8th mag. stars) on the half-frame on which it first appears. Mag2 is the estimated magnitude a half-frame, or 1/60th second, later. The main part of flash B probably occurred during a brief dead time between the half frame of "Mag1" and "Mag2" since it appears signifigantly brighter, about 4th or 5th mag., on Sada's tape. In all cases I can't see any evidence of the flash in the half-frame 1/30th second after the first one, except for D, where it seems to appear there at about 9th mag. The selenographic locations should be accurate to within 1 deg. or 30 km. Their locations were recently improved by using a grid overlay. All of these are in the western part of Oceanus Procellarum (Ocean of Storms) except D, E, and G, which are in highlands area a short distance west of the western shore of Oceanus Procellarum. The times have been determined by Don Stockbauer, Victoria, Texas, after creating an accurately time-inserted copy using an IOTA-Manly video time inserter. Event G was found by Peter Gural, SAIC, on my videotape and was confirmed by David Palmer on his tape. Images of it will be added later.
Observer Information West Telescope Name Location Long. Lat. Aper. Recording B. Cudnik Columbus, TX 96.664 29.618 36cm Audio tape (vis.) D. Dunham Mount Airy, MD 77.206 39.342 13cm PC-23C videocam R. Frankenberger San Antonio, TX 98.653 29.486 20cm PC-23C videocam D. Palmer Greenbelt, MD 76.859 38.988 13cm PC-23C videocam P. Sada Monterrey, Mex. 100.143 25.915 20cm PC-23C videocam Observer Contact Information Name Institution E-mail Brian Cudnik Prairie View A&M Univ. cudnik@cps.pvsci.pvamu.edu David W. Dunham JHU - Applied Phys. Lab. dunham@erols.com Rick Frankenberger Univ. Tex., San Antonio rickf@stic.net David M. Palmer Goddard Space Flt. Ctr. David.M.Palmer.1@gsfc.nasa.gov Pedro Valdes Sada Universidad de Monterrey psada@ix.netcom.comD was the brightest impact. Besides Palmer's and my videotapes, it is also in videotapes by Pedro Sada and by Rick Frankenberger in San Antonio, Texas. My image for the event also shows three stars, from north to south (right to left in the image) being 7.6- mag. SAO 146577, 8.2-mag. SAO 146578, and 8.9-mag. SAO 146574, all of whose occultations were recorded a few minutes later. The first two stars are also visible in David Palmer's frame of the D impact. Some of Palmer's images are on the IOTA Web site at http://www.lunar-occultations.com/iotaSada reports two more events estimated at about 5th magnitude at 4:32:50.8 and 4:34:49.7 UTC, but they have not been found in other tapes (the field of view of my 5-inch telescope used for the 6 known events was aimed at a more southern part of the Moon than usual, so they would have been missed if they occurred a little north of the equator). The 2nd event was fairly close to the terminator. Other possible unconfirmed events (some chance of their being videotape defects) were recorded by me at 4:50:15.9 UTC and by David Palmer at 2:42:02.
In late July, Peter Gural used a digitized version of my main two videotapes of the Moon's dark side on 1999 Nov. 18 UT to determine the magnitudes of the impact flashes; his results are given below, for the new events as well as in the table above of the confirmed impacts. In addition, I have found the new impacts that he found on the time-inserted copy that Don Stockbauer made, so I give below accurate times for those events, accurate to a few hundredths of a second [I have not applied the small rate and light propagation time (from Ft. Collins, CO) of WWV]. I also give approximate locations for the last 3 events, so that and the good times should aid others in locating these in their tapes for possible confirmation. The brightest flashes are fainter than I expected; I suppose that when one does see a very brief flash like these, the subjective impression (from contrast) is that they appear brighter than they really are.
New Probable Impact Flashes Univ. Time mag. approx. location ---------- ---- -------------------- 1:46:09.67 6.7 2:52:19.68 8.3 [some doubt] 4:40:26.75 6.3 long. 70, lat. 15 N. 4:51:24.92 6.3 long. 80, lat. 45 N.* 5:26:43.25 5.3 long. 60, lat. 0* This one is very close to the edge of the Moon. What appears to be a bright noise spot is close to the 2nd event on the same frame, so I am dubious about it. The last event occurred only about a minute before the end of my 2nd tape. That will encourage me to look at a short 3rd tape that I made for about 20 more minutes, until the Moon set into trees at an altitude of about 3 deg. above the western horizon at Mt. Airy. Peter notes that all of the impacts have distinctive round images like stars and unlike several noise spikes, all elongated and usually in just one horizontal line, that are also on the tape. His images of these flashes can be seen here. After determining the time of the G impact, I scrutinized the tape more carefully visually for +/-10 seconds or so. I found what looks like another faint impact flash at 4:12:26.03 U.T. (that is, 1.80 seconds earlier than the flash described above). It is at about the same "latitude" as the above event (40 to 50 deg. south, I'd estimate), but well on the Moon's dark side a few minutes of arc in from the edge. It has a signal-to-noise ratio of only about 3 (probably below the threshold of Peter's software) and occupies a few pixels on each of two rows. But, Peter Gural only found it one time; the event remains unconfirmed. Jay Melosh, at the University of Arizona's Lunar and Planetary Laboratory, calculates that the mass of the impacting meteoroids ranged from several tens of kilograms to a few hundred kilograms (hundreds of pounds) and that they were about half a meter (or one to two feet) in diameter. The resulting craters are probably 10 to 15 meters (30 to 50 feet) in diameter. However, such large bodies in the Leonid meteor streams are thought to be significantly rarer than the new lunar observations imply. Mark Matney, of Lockheed Martin Space Operations in the Orbital Debris Program Office at NASA Johnson Space Flight Center notes that much more energy was converted into light than expected from standard theories during artificial satellite collision tests. Matney believes that hypervelocity collisions may produce some non-equilibrium phenomena that produced the extra light. So the meteoroids causing the observed lunar impacts may be ten to a hundred times smaller than Melosh indicates, making them more compatible with the expected Leonid stream distribution. More recent work seems to confirm this. Although certainly not visible from the Earth, the new craters might be found by comparing new images that will be obtained by the Japanese Selene spacecraft, scheduled for launch in 2003, with Apollo or Lunar Orbiter photoes taken about thirty years ago.Sunglints, caused by sunlight briefly shining off of artificial satelites or space debris, have been proposed as a possible explanation of the flash observations. This is very unlikely since the observations were made late at night local time when most orbiting space objects were deep in the Earth's shadow. Geosynchronous satellites are high enough to be outside of the Earth's shadow. But none of these were close to the Moon as seen from Mt. Airy at the time of the A-impact as shown in this view of them provided by Sam Herchak, Mesa, Arizona (the time on the figure is MST). Another strong argument against sunglints, pointed out by Paul Maley, is their short duration. Most sunglints are a few tenths to even seconds long as an artificial satellite slowly rotates. For a sunglint to be only 1/30th of a second, since the Sun's angular diameter is 1/2 deg., this would mean that the satellite must be rotating a full revolution every 12 seconds. For a satellite outside of the Earth's shadow as seen from Mt. Airy, Maryland when the lunar flashes were recorded, the geometry could not change significantly in 12 seconds, so there would be another similar flash 12 seconds after the first one, and probably several more. But we have looked at the tapes for over a minute from the times of the observed flash events, and we see no other flashes, certainly not like the reported ones. Also, sunglints vary in time with location on the Earth, while the flashes that we observed occurred at the same time at the different locations, as they must if they are lunar impacts. Also, with six flashes simultaneously recorded at two or more separated locations, the chances are much greater that the flashes are lunar phenomena than something closer. When lunar location information is available in the separate video records (in two of David Palmer's images), there is also agreement to within the measurement accuracy of about 2 degrees. From David Palmer's video images, the selenographic longitude and latitude of the D impact were 68.5 degrees west and 2 degrees north, respectively, while for the E impact, these values were 79 degrees west and 17 degrees south, respectively.
David Dunham, IOTA, 1999 December 3; revised, 2000 May 1, Sept. 15 and 22
